Where king may be lying about current grand cause (9)
I believe the answer is:
instigate
'where king may be lying' is the definition.
The definition suggests a singular noun but the answer is not.
'about current grand cause' is the wordplay.
'about' indicates putting letters inside.
'current' becomes 'I' (symbol for electric current).
'grand' becomes 'g' (G is short for grand as in a thousand).
'cause' becomes 'instate' (I can't explain this - if you can you should give a lot more credence to this answer).
'i'+'g'='ig'
'ig' placed into 'instate' is 'INSTIGATE'.
Can you help me to learn more?
(Other definitions for instigate that I've seen before include "I get saint to urge or incite" , "Provoke" , "Incite - set in motion" , "I taste gin to incite or urge" , "Start" .)